In photovoltaic power systems, it may be necessary to ground one power terminal of a photovoltaic array to comply with regulations, for example UL1741 or to comply with manufacturers recommendations (some thin-film modules). These systems may either be positively grounded or negatively grounded at a single point.
During the operation of grounded PV systems it is possible for a fault to develop which acts as a second grounding point for the array. Depending on the location of this fault, large ground currents may flow. This is a potentially dangerous situation therefore the ground fault current must be interrupted. Interruption of the fault current is typically achieved by disconnecting the original grounding point. A ground fault indication is made and the inverter associated with the PV system is disabled at this time so that the ground fault can be rectified as soon as possible. The grounding of the array, interruption of fault current, and indication that a ground fault has occurred (the indication of which is used to disable the inverter and alert a user) are achieved by a Ground Fault Detection and Interrupt circuit (GFDI).
Components of such systems must undergo rigorous testing before being approved for use. In the US the Underwriters laboratory standard UL1741 ‘Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources’ is required by the inverters of most photovoltaic installations. Typically, such systems are tolerant only of DC voltages up to 600V however there is a demand for 1000V listed products. To simplify the approvals process it is desirable that components listed by US national test laboratories are used. However due to other US standards (e.g. UL508A) such components are typically listed for DC voltages of a maximum of 600V.
Accordingly, there is a need for a UL1741 compliant, high voltage tolerant GFDI system. To minimise the testing required for such a system it is desirable that it is constructed using components listed by US national test laboratories.